A Sunday at the Pool in Kigaliby Gil Courtemanchetranslated by Patricia Claxton£14.99, Canongate, 258pp

A couple of years before the genocide, I left my parents' house and crossed the Uganda border in a bus bound for the Rwandan capital, Kigali. All summer we'd watched lorries full of munitions pass by on the same road, stirring up clouds of red dust. Sometimes they carried French arms for the Hutus; sometimes it was British arms for the Tutsis. There was something going on, and I wanted to see for myself what it was.

Reaching Kigali, I stayed in a hotel called the Mille-Collines: the same place that provides the opening scene of the Canadian writer and film-maker Gil Courtemanche's astonishing first novel, A Sunday at the Pool in Kigali. We were probably guests at the same time. By then the killings had already begun: the first small drops of the coming blood-dimmed tide.

Against such a background, treading the margin between actuality and its representation is a delicate business. So it is important, as I can vouch, that the images of Courtemanche's opening are utterly authentic. Round the pool congregate: French paratroopers with shaven heads and something of the vulture in the way they watch female flesh; prostitutes rife with Aids; a grandly parading Rwandan bigwig back from Paris, with a sporty outfit "so new its yellows and greens are blinding, even for sunglass-protected eyes".

Courtemanche's novel conveys the pressure of lived experience very powerfully; yet at the same time experience is clearly mediated by a sophisticated literary imagination. His time in Rwanda, where he worked as a journalist, may have produced the first great novel of the catastrophe that befell that country, but its literary qualities are what count, not their context.

If it is to be considered a historical novel, it is one of a peculiar kind, dedicated as it is to many of the characters who actually appear in the book, most of whom are now dead. One is Gentille, a waitress at the Mille-Collines who served Courtemanche "eggs and beer and could be dead or alive, if only I knew". Those who planned and conducted the genocide are also identified by their true names.

A slightly different Gentille - a little smudging here - is the novel's heroine. She has a secret. For several generations her Hutu family, unaccountably tall and pale-skinned, have been masquerading as Tutsis, taking advantage of the superior position the latter tribe used to hold. Now the tables are turned and Gentille's features mean she is being penalised for being the Tutsi she actually is not.

Courtemanche's alter-ego, a Canadian documentary-maker called Valcourt, falls in love with her. He is a somewhat cynical character, especially about development workers and the new UN general who arrives smelling of Brut: "an eau de Cologne highly prized by the military and the police". But Gentille awakens a love in him of an erotic fervour that is almost holy in its intensity, to the extent that at first he cannot make love to her.

Everywhere else, sex and death obtain, often at the same time. In one scene - moving, comic and horrifying all at once - Valcourt films the death of his friend Méthode from Aids. Méthode's mother, his brother Raphaël and various others attend to watch as a prostitute gives him one last orgasm. A friendly nurse has administered vials of morphine and a huge glass of whisky. As Méthode whispers to Raphaël: "Even rich people in the United States don't have beautiful deaths like this."

Another death is more troubling. Valcourt's friend Cyprien (one of those to whom the novel is dedicated) is forced to have sex with his wife as Hutu militiamen slash them with machetes. "Wife, better to die of pleasure than of torture," he says, as his passion and enormous erection raise the interahamwe to murderous fury. It is a moment of Shakesperean intensity: the Shakespeare of Titus Andronicus rather than the Shakespeare of As You Like It.

There are many such shocking scenes: another describes a pregnant diplomat's wife being serviced by a pool attendant with Aids. She gives birth in the poolside shack shortly after climaxing. The umbilical cord is cut with a Swiss Army penknife. To those readers who will say to Courtemanche that he has an overactive imagination, he retorts (in his introduction): "They are sadly mistaken." Yet there is also much tenderness and humour in this book, as when Valcourt reads Eluard poems to Gentille under a fig-tree by the pool, and then makes love to her for the first time. "Make me come again with words... I want to read everything your Monsieur Eluard has written." Soon afterwards they get married.

The idyll cannot last. When Valcourt tries to escape to Nairobi with Gentille, she is kidnapped and disappears. The book ends with a short piece of writing by her in an exercise book - 50 or so pages lined in blue with "a pink vertical line indicating the margin" - that he discovers later. It is a heartbreaking valediction to both Valcourt and the many readers this novel deserves.